


I Love You

by Flamour



Category: Undertale (Video Game)
Genre: Future Mpreg, Kidnapping, M/M, Non-Consensual Drug Use, Possible Character Death, Tattoo, Yandere Sans
Language: English
Status: In-Progress
Published: 2016-04-18
Updated: 2016-04-18
Packaged: 2018-06-03 02:19:11
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 5
Words: 3,993
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6592642
Author URL: https://archiveofourown.org/users/Flamour/pseuds/Flamour
Summary: <blockquote class="userstuff">
              <p>When underswap Sans met underfell Sans, he immediately knew they had a connection. They were soul mates, now he just had to make the other understand,</p>
            </blockquote>





	1. The Capture

When Sans had asked his brother about love, Papyrus had been confused. Was his brother interested in someone?

“well bro, ya know ya love someone when your heart beats faster around em. or when ya’d do anythin for em, and ya wanna make em happy. ya wanna protect em from whatever’ll harm em. does that make sense?” Sans had nodded and asked another question.

“So I have to make sure they’re safe and happy?”

“well ya.”

“Oh thank you, Pappy! The magnificent Sans can take it from here!” And that was that. Sans had begun preparing right away, adding some new trinkets to his speed boat themed bed, asking Papyrus if they could do story time in his room instead, and getting some medicine from Undyne. The scientist said it was a special medicine to calm her experiments, so with permission he took enough to last quite a while. Anything to make his love feel better.

That was another thing, his love. Recently he had fallen for someone he met at a Christmas party. Underfell Sans, or Fell, he quickly stolen his heart with his rugged charm and controlling demeanor. They had hit it off in Sans’s opinion. He knew the other loved him too, how could he not?

Everything ready, he waited for Papyrus to leave for work before contacting his other self. Each Sans had special phones in order to communicate, science Sans having gifted them at Christmas. Quickly shooting a text reading ‘emergency, help!’, he waited.

Sans was making tacos when he heard the front door bang open and a loud voice call, “What the hell’s goin on? Who do I need ta fuck up?”

Giggling to himself he responded. “Pappy left early today, and I made too many tacos, so you’ll just have to help me eat them!”

“Dammit Blue, this is not an emergency!” The other groaned, taking a seat at the table and putting his skull in his hands.

“Well you’re here now, so eat up!” He placed a plate in front of Fell, stocked with two tacos made exactly how he knew the other liked.

“I don’t got time for this! I need ta head back or Boss is gonna have my ass for slackin off.” Sans frowned. His love wanted to leave him, and wouldn’t eat the food he worked so hard on? He couldn’t have that. “What the fu-”

Using his magic he secured the other’s arms and legs to the chair, smiling when all attempts to escape were for naught. “You can’t leave yet, you haven’t eaten!”

“Blue,” the darker skeleton growled, “I’m not hungry, let me go.”

“You’re not being very nice. I worked hard on these. Oh! Maybe you just need some medicine! That’s what Undyne does.” Ignoring his shouting and cursing captive, he rushed to his room and picked up a vial of liquid. There were many more, so he could use as much as needed. Just one vial would be enough to keep the other pliant and a little sleepy.

Arriving back to the kitchen he poured the poison over the tacos like a sauce. “There! Now, eat up!” He held one of the tacos to Fell’s mouth and frowned when the other kept his mouth stubbornly closed. “Come on, they were made by the magnificent Sans, they’re good I promise!”

“I’m not eating poisoned shit you little-”

He didn’t let him finish, stuffing a bit passed his teeth and watching as they closed automaticly, successfully taking a bite.

Fell swallowed hurriedly. “Fucking stop-” another forced bite, another swallow. He didn’t open his mouth again.

Sans pouted and stomped his foot. “Why are you being so stubborn?! They taste great, right?”

“Thats not the fucking point-” another. His captive grunted in frustration. “What are ya doin this for anyway?” Bite, swallow.

“I love you, silly! I know you love me too, so I asked Pappy what people in love do. He said people in love protect each other, and make each other happy,” Fell was starting to feel the affects of whatever toxin was given to him. His very bones felt tired, and he couldn’t drudge up any of his magic. What was the innocent blueberry doing with this strong poison? “So I, being as magnificent as I am, brought you here so I could take care of you from now on. You’re going to love it here, I just know it!”

“W-what the fuck? I don’t love ya, ya little weirdo! Yer alright, and I’d even call us friends, but I don’t love ya! Now let me go, I have ta get back before Boss notices I’m gone.”

“You don’t have to lie anymore, it’s OK! Now, let’s go to our room where we can be more comfortable.” Not waiting for the other to respond, he released the magic holding his captive in place. Using a surprising amount of strength Sans swept Fell into his arms and up the stairs to his room. “Easy now,”

The soft mattress was a relief to Fell’s drugged bones, and he sank into the bed sheets gratefully. Only to be brought back to reality by the feeling of cold metal surrounding his wrist. Glancing down at his right hand he saw a thick steel manacle connected to a chain that lend under the bed.

“Are ya serious?! Why are ya doin this?”

Sans sat beside him and smiled. “I wouldn’t want you to leave and get yourself hurt! I usually dislike naps, but you seem a bit tired. Rest, Sweetie.“

Fell sputtered at the pet name, but Sans had already left, closing and locking the door behind him. “What the hell have I gotten myself into?”


	2. The Hunger

It had been three days since Fell kidnapped. He remained bound to the bed by the anacle around his wrist. The poison, it turned out lasted for five days. It effects only weakened by some, but not enough. It wouldn’t matter anyway. Since his first drugged meal, Fell refused to touch anything made by Sans.

_“I made you some tacos, Sweetie! I know how much you loved yesterday’s so I made some more!” His captor called, entering the room and locking the door behind him._

_“M'not eating anymore of your poisoned shit!” Sans pouted at the refusal before smiling brightly again._

_“That’s okay! I’m sure you’ll change your mind soon~“_

Sans had set the plate of corrupted food next to his computer, just out of Fell’s mobility. He hadn’t eaten since, and it was starting to show. His usually plump crimson stomach was now a sad little sack, empty of desperately needed nutrients. Even as the poison in his bones lightened up, the starvation mad fit impossible to do anything about his current situation.

Sans seemed to notice this, stroking his captive’s skull in unwanted comfort during the times his stomach would growl.

During these three days, Sans himself was scarce. He only appeared at ‘bed time’, cuddling the other close and falling asleep, only to be gone again when Fell woke up. It was disconcerting to day the least.

Sans, on the other hand, was very busy. During the first day, he decided to ask Papyrus what collars were for. He’d seen them in some of Undyne’s anime, and was afraid he was missing a crucial step.

“Pappy!”

“ya, bro?” They we’re sitting on the couch, watching what seemed to be a game show with random questions. Any other time he would be absolutely absorbed in the host’s antic, but he had questions that needed answers.

“What are collars for?”

“uh…why?”

“Sometimes the couples in anime wear them. Are collars important to showing love?”

“well no, not really.”

“Then what are they for?”

“well, I guess it’s a way of showing ownership? there’s collars, piercings, tattoos. not all couples do it though..”

A tattoo? Oh that sounded wonderful! He could put something pretty on his love, and then everyone would know they were together. As soon as Fell was out of denial and ready anyways.

“Do you have any? Well obviously you don’t have a collar, but a piercing or tattoo?” His brother chuckle and pulled him in for a hug.

“got a tattoo when we first moved here, wanna see?” Sans eagerly nodded and watched as Papyrus pulled of his sleeve to the elbow. There, on the back of his arm was a silver engraving of one of has blasters. “cool huh?”

“Wowzers! Did it hurt?” He gingerly traced over the mark with small fingers.

“ya, but if my brother’s so cool, I gotta be cool enough to handle it. right?”

Sans chuckled before hugging his brother tight. “You’re so cool Pappy. Not as great as I, the magnificent Sans, but still cool!”

“thanks, bro.”

After that, Sans watched the rest of the show with his brother. After it ended, he told Papyrus he was going to patrol for any humans. The older just nodded and wished him luck.

He felt bad about lying, but he needed to see if the Floweys had anything. Entering their village he was greeted with the usual round of ‘Howdy’s. Returning the greetings he entered the store.

“Howdy! What can I get for you?”

“I need something to tattoo a skeleton.”

“Oh! I still have the machine your brother used, would you like that?”

“Yes please! Does it come in blue?”

Making his purchase he thanked Flowey and make his way home, prize in hand and humming happily. The whole trip took most of the day, and he arrived just in time for his bed story.

He quickly hid his new treasures in his room, ignoring Fell. While listening to his brother’s soothing voice, he thought about what tattoo would look the best on his lover, finally settling on a star. The star itself was half blue, and half black with small random designs surrounding it.

When Papyrus had finished the story, Sans gave him a big hug and a chipper ‘Thank you, Brother!’ Before finally settling in his own bed. He pulled Fell close and closed his eyes.

“Please…please Sans. Please just a little bit…I’ll eat anything. I’m so hungry…please.”

With a smile on his face he ignored the desperate whispers and pulled his mate closer.

**Notes for the Chapter:**

> Visit my Tumblr! https://www.tumblr.com/blog/flamourlegends
> 
> Sorry for any mistakes!


	3. The Tattoo

When next Fell awoke, Sans was sitting on the edge of their bed and petting his skull. Flinching, he caught the most amazing scent, but was too weak to investigate. instead he turned his attention to his captor. The other smiled widely, stopping his petting in favor of bringing that tantalizing smell closer.

“Are you hungry? I brought some breakfast for you!” He couldn’t even bring himself to lean up and take the plate. “Oh! Don’t push yourself sweetie, i’ll feed you. Pappy says that’s what couples do sometimes.”

He was helped into a sitting situation, the other proceeding to feed him his first meal in three days. He didn’t care about the poison anymore, he was just so grateful to have something in his stomach. He was extra thankful for the glass of milk he was offered. He was slightly dissapointed when the food was gone.

“I have a surprise for you!”

“O-oh?” He watched as Sans collected a medium sized box and returned to his side.

“I’m gonna give you a tattoo!” Sans was obviously excited, Fell less so.

“What?!”

“Cool right? My brother has one, and he told me that sometimes couples would get one to show they were together.” He was removing the supplies from the box now, ignoring the suddenly struggling Fell.

“What the fuck? I don’t wan’ a tattoo, ya freak!” Despite his harsh words and halfhearted struggles, Fell knew he would never have enough strength to escape. “C-c’mon man, ya can’t be serious!”

“Of course I am, silly! Don’t worry, it’ll look really cool!” Sans’ magic forced Fell spread eagle on the bed, the blueberry regarding his captive with a pensive expression. “Now where should it go…”

“How’s about no where?”

“Oh don’t be such a sour bones! Ah!” Fell’s shirt was removed quickly and efficiently. Sans stroked his scapula thoughtfully. “This looks like a nice spot, don’t you think?”

“No!”

“Great! Please hold onto this, don’t want Pappy to wake up.” His shirt was stuffed into his mouth, then covered by tape. “Now it’ll stay in. You don’t wanna accidentally spit it out, right?”

“Mff!”

“Exactly! Now, let’s get started. I made the stencil while waiting for you to wake up, you lazy bones! Honestly, I thought you were going to sleep forever.” The stencil was applied easily, the binding magic not allowing him any wiggle room. He watched as Sans dipped the needle in ink before bringing it to his bone. “Don’t worry, it’ll be done soon!”

soon, it turned out, was six hours later. amidst the tears and grunts of pain were soft reassurances and compliments. just as Fell was starting to wonder just how much he could take, it finally ended. His eyes had been shut tight in a failed attempt to block the pain, but finally opened now that the torture was over. He watched with watery eyes as Sans packed away the materials and acquired a wet hand towel.

“Lets wash that dust away, shall we?”

Fell whimpered at the touch, his bones sore and tender. The washing was over with fast thankfully, and he could only stare when Sans held up a mirror, angled to show his brand new tattoo.

“What do you think? Doesn’t it look great?” He had to admit, it was pretty damn cool, and maybe he would’ve gotten it under different circumstances. Either way he couldn’t respond, his mouth still stuffed and shut tight. Sans wasn’t deterred by his lack of enthusiasm. “Now everyone will know we’re together!”

Fell couldn’t stop the new tears from falling. he really wasn’t leaving…was he?

**Notes for the Chapter:**

> Visit my Tumblr! https://www.tumblr.com/blog/flamourlegends
> 
> Sorry for any mistakes!


	4. The Walk

“Sans,”

“Yes, sweetie?” The sponge running over his arm traveled to his shoulders, being careful of the newly acquired tattoo. He shivered a bit, but otherwise stayed still. He was trying to convince the other to let him outside for a bit. It wouldn’t do to get on his bad side.

“W-well i’ve been inside fore a while now, and i’m kinda goin crazy.” When the scrubbing paused he was worried he’d messed up, but it slowly resumed. “I-it’ll only be a few minutes, i wont go anywhere, i swear! I just need some air, y’know?”

“I guess it would be uncomfortable to be stuck inside. Alright! You can go outside today for a bit, but if you’re too sleepy from the medicine you come right back okay?” They finished with their bath and got dressed, Sans insisting on helping Fell.

“S-sure.” With one last look at his captor, whom headed straight to the kitchen, Fell took his first steps outdoors since his capture. He wanted to run, to find help. But he knew he had to wait, Sans would be expecting him home, and no doubt would come looking if he were to be late for dinner.

He trekked through Snowdin, noticing all he differences from his own universe. He passed Muffett’s bakery, not really having an appetite. Sans always made sure he ate his fill now that he could eat again. There was burgerpants, selling his burgers up ahead. Deciding to talk to him for a bit, he approached unaware of the eyes following his every move.

“Hey there stranger.”

“Hey little fella, how are you doing today?” The cat monster scratched himself behind the ears, giving Fell a bright smile.

“Oh y’know, as good as any skeleton in this cold.”

“The wind going right through you?” Fell laughed for what seemed like the first time in forever. He didn’t notice the eyes that had been watching him were now glaring daggers at the salesman.

Sans’ p.o.v

When Fell had left, Sans hurried to follow after. He watched from a distance as his lover passed the bakery, and greeted Burgerpants. His eyes narrowed when Fell started laughing at the other monster’s joke. What was happening? This wasn’t how love worked! Why was he laughing at someone else’s joke? Sans was the only one who could make his love laugh like that. Giving a dark glance at the sales monster, he watched as Fell made his way home. He would join him soon.

He had something to do first.

Fell’s p.o.v

He didn’t know what to do. It seemed Sans had left for a few errands, as a note on his door indicated, so Fell had taken a seat on the couch and decided to wait. It wasn’t long before he heard the front door opening and closing. He startled as Sans took a seat next to him and leant into his side.

“How was your walk?”

“I-it was nice.”

“Good! Maybe you can go out again tomorrow.”

He was offering more freedom? “Really?”

Sans nodded happily. “Of course! Now, stay here while i make some dinner. Pappy is staying at Muffett’s tonight, so we’ll have the house to ourselves.” He did just that while Fell watched in confusion. Was it just him, or did the blueberry seem a little tense?

He’d made it through one movie and halfway through another when Sans appeared with dinner. They ate on the couch together, even if his food was drugged he’d rather not be starved again. That was not an experience that needed repeating. When they were finished, Sans took their plates to the sink before returning to his spot wedged into the darker skeleton’s side.

“I heard you were talking to burgerpants today.” there was something dark in his tone, something that didn’t belong there.

“Y-yeah. He’s a pretty funny guy…”

“Mmm. Let’s go to bed, shall we?”

“U-uh ok?”

Sans somewhat roughly led him to their room, shoving him inside. He forced his love’s wrist into the manacle and down onto the bed.

“H-hey, what’s goin on?” Sans didn’t respond at first, choosing to get in bed and curl up to his captive’s chest and gently finger the tattoo.

“That’s not how love works, sweetie. You’re not supposed to laugh like that for others, only me.”

“What the fuck?” A growing sense of dread filled him.

“But that’s okay, you don’t have to worry about him anymore sweetie! I took care of it.” He nuzzle’s his lover’s sternum, giving a content hum and completely oblivous to the other’s horror.

“Oh god…what did you do?” His trembling words never reached Sans.

He was already asleep.

**Notes for the Chapter:**

> Visit my Tumblr! https://www.tumblr.com/blog/flamourlegends
> 
> Sorry for any mistakes!


	5. The Knowledge

Just like every other morning, Sans made breakfast for his brother while they watched a special news report on the tv. It seemed someone had found Burgerpants’ stall burned and wrecked, the cat monster nowhere to be found. Dust or whole. Despite the awful news, Papyrus left for work as usual while Sans brought a plate up to his room where he set it on the table next to where Fell lay sleeping. He stroked the other’s skull softly, listening to his soft snores, before heading out.

He had big plans today, something to help improve their relationship. He’d hears Alphys mention it before and decided he would check the library for any info he could find. With a big smile on his face and a bounce to his step he approached the librarian.

“Hello! Do you have any books about sex?”

The librarian, who had been reading, dropped her boom and stared at the town’s resident innocent marshmallow.

“Um, did I not say it right? Sometimes Alphys says mating. Is that it?”

The worker silently, and somewhat shakily, gestured to a bookshelf in the far back. What would Papyrus think of her, showing his little brother such inappropriate books?

She wouldn’t have to wonder long, however, as she saw the mentioned older brother passing by and spotting his sibling. Papyrus was at his brother’s side in a blink, looking over the oblivious skeleton’s shoulder as he read.

“hey bro, what ya readin?” The smaller skeleton startled before looking up with an innocent smile.

“Hi Pappy! Alphys said something about mating and sex, and how it helped her and Undyne’s relationship!”

Papyrus could swear he felt his eye twitch. “oh did she now?”

“Yeah! I wanted to try it, but I don’t know what it is, so I came here to find out!”

“wow bro, that’s really smart. hey, I wanna meet thus friend you have first though. don’t ya think we should be friends if you’re gonna mate him?” Sans eyes turned into stars, glowing in his excitement.

“That's a great idea Pappy! And maybe after you meet him, you can tell me what sex is?”

Papyrus have a nervous ‘sure, bro’ before getting dragged along to their house. “wait, they live with us?” His only answer was an energetic nod and a hand tugging at his sleeve.

Dropping his hold on Papyrus’ hoodie, Sans opened his door softly and peeked in. Fell was still asleep, so Sans and Papyrus quietly entered the room, the older brother stepping closer to see their guest.

And the uncovered manacle.

“bro, is this fell? he’s the one ya like so much?”

“Don’t be silly brother! I don’t like him, I love him. And he loves me too!” Sans, though excited, kept his voice down so he didn’t wake up his lover. “Will you tell me what sex and mating are now?”

“why don’t you go ask undyne? I’m sure she can tell you everything. I’ll stay and bond with fell here while you’re away.” He gently touched the manacle, turning it -and the arm attached- around to get a better look. The bone was somewhat scuffed up from last nights rough treatment.

Sans gasped in delight and hugged his brother. “You’re so smart Pappy! I’m gonna go now, can you stay here with him?”

“sure bro.” He’d barely spoken when Sans was out the door and leaving the house. Papyrus smiled at his brother’s energy, before turning his attention to the sleeping skeleton. “What has my brother gotten himself into?”

with sans

Using the river person, and just plain excitement, Sans arrived at the lab in no time. He knocked on the door and called out. “Undyne, I have some questions!”

The door opened to reveal the timid scientist. “Sans? W-what kind of questions?”

“What’s sex and mating?”

“O-oh dear…”

with Papyrus

When he was sure his brother was gone, Papyrus gently shook the sleeping skeleton’s shoulder. He was greeted with sleepy eyes, which quickly widened in panic and slight hope. “hey there, buddy.”

“P-please! Get this off, let me go! H-he’s gone crazy!” Fell practically threw the arm attached to the cuff in the taller’s lap.

“woah, calm down. what happened?”

“He texted me that there was an emergency a few days ago, then made some shitty comment about making too much food. When I tried to leave, he poisoned the shit and forced me to eat it! Your brother’s gone crazy!”

“tell me everything.” He commanded. Commands were good, Fell was used to those from his own Papyrus. He easily complied, telling the other everything from the start.

with Sans

“…you understand?” They we’re sitting up stairs on the unfolded bed, eating ramen while Undyne answered his questions.

“Yeah! So then, what’s mating?” He put his now empty ramen bowl on a nearby table.

“Its pretty much the same thing, but before you -ahem- climax, you mark your lover and put a bit of magic into their soul. Sometimes babies are made as a result though, so I’d be careful.” Sans tilted his head in thought.

“Mark…like biting?”

“Exactly. Uhm, is that it?”

with Papyrus

“look, I know what he’s doing is wrong, but give him a chance? this is the first time I’ve seen him so happy.”

“it’s not like I have a choice…”

“thanks bud.“

with Sans

"I read babies bring a couple closer together.”

“Y-yes I suppose.”

“Wowzers! How do I make one?”

**Notes for the Chapter:**

> Visit my Tumblr! https://www.tumblr.com/blog/flamourlegends
> 
> Sorry for any mistakes!

**Author's Note:**

> visit my tumblr! https://www.tumblr.com/blog/flamourlegends
> 
> Sorry for any mistakes!


End file.
